International TechNet Wiki Summit2015

Saeid Hasani

Structured Error Handling Mechanism in SQL Server 2012 & 2014

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Senior Database DeveloperSQL Server ConsultantFreelance SQL AuthorT-SQL TrainerTechnet and MSDN SQL Server Forums Moderator

Saeid Hasani

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TRY• Try executing statements  CATCH• Handle the errors if they occur

Is there any structured Error Handling mechanism in SQL Server?

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Is there any structured Error Handling mechanism in SQL Server?

BEGIN TRY -- Start to try executing statements SELECT 1 / 0; /* Executing statements */END TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs PRINT 'Error occurs!' /* Handle the error */END CATCH -- End of Handling the error if occurred

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Is there any structured Error Handling mechanism in SQL Server?

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Will all statements in TRY block try to execute?

BEGIN TRY -- Start to try executing statements PRINT 'Before Error!' -- Statement no1 SELECT 1 / 0; -- Statement no2 PRINT 'After Error!' -- Statement no3END TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs PRINT 'Error occurs!' /* Handle the error */END CATCH -- End of Handling the error if occurred

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Will all statements in TRY block try to execute?

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Does the CATCH part automatically handle the

errors?

BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- StatementEND TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs END CATCH -- End of Handling the error if occurred

Does the CATCH part automatically handle the

errors?

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Does the CATCH part automatically handle the errors?

TRY• Try executing statements CATCH• Handle the error if occurs• RAISERROR

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Does the CATCH part automatically handle the errors?

BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- StatementEND TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs RAISERROR('Error!!!', 16, 1);END CATCH -- End of Handling the error if occurred

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Does the CATCH part automatically handle the errors?

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Does the CATCH part automatically handle the errors?TRY• Try executing statements CATCH• Handle the error if occurs• RAISERROR• ERROR_NUMBER()• ERROR_MESSAGE()• ERROR_SEVERITY()• ERROR_STATE()• ERROR_PROCEDURE()• ERROR_LINE()

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Does the CATCH part automatically handle the errors?BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- StatementEND TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs DECLARE @ErrorMessage NVARCHAR(4000); DECLARE @ErrorSeverity INT; DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. );END CATCH -- End of Handling the error if occurred

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Does the CATCH part automatically handle the errors?

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Is it a good idea to use a general procedure as a

modular Error Handler routine?CREATE PROCEDURE spErrorHandlerASSET NOCOUNT ON; DECLARE @ErrorMessage NVARCHAR(4000);DECLARE @ErrorSeverity INT;DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. );

Is it a good idea to use a general procedure as a

modular Error Handler routine?CREATE PROCEDURE spTestASSET NOCOUNT ON;BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- StatementEND TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs EXEC spErrorHandler;END CATCH -- End of Handling the error if occurredgo------------EXEC spTest

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Is it a good idea to use a general procedure as a modular Error Handler routine?

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Is it a good idea to use a general procedure as a modular Error Handler routine?CREATE PROCEDURE spTest AS SET NOCOUNT ON;BEGIN TRY -- Start to try executing statements SELECT 1 / 0; -- StatementEND TRY -- End of trying to execute statementsBEGIN CATCH -- Start to Handle the error if occurs DECLARE @ErrorMessage NVARCHAR(4000); DECLARE @ErrorSeverity INT; DECLARE @ErrorState INT; SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY(), @ErrorState = ERROR_STATE(); RAISERROR (@ErrorMessage, -- Message text. @ErrorSeverity, -- Severity. @ErrorState -- State. ); END CATCH -- End of Handling the error if occurred

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What are the benefits of THROW

when we have RAISERROR?

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1. Correct line number of the error!

CREATE PROCEDURE spTest AS SET NOCOUNT ON;

BEGIN TRY SELECT 1/0END TRYBEGIN CATCH declare @msg nvarchar(2000) = error_message();

raiserror( @msg , 16, 1); THROW END CATCH

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2. Easy to use

Another benefit of using the THROW statement is that there is no need for extra code in RAISERROR.

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3. Real Terminator!

BEGIN CATCH DECLARE @msg NVARCHAR(2000) = ERROR_MESSAGE(); RAISERROR( @msg , 16, 1); ----------------------------- CREATE TABLE #Saeid (id INT) INSERT #Saeid VALUES ( 101 ); SELECT * FROM #Saeid; DROP TABLE #Saeid; ----------------------------- THROW PRINT 'This will never print!!!';END CATCH

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4. Independence of sys.messages

CREATE PROC sptest AS SET NOCOUNT ON;BEGIN TRY SELECT 1/0END TRYBEGIN CATCH THROW 60000, 'This a custom message!', 1; END CATCH

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4. Independence of sys.messages

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I want to check a condition in the TRY block. How

can I control the flow of execution and raise the

error?CREATE PROC sptest AS SET NOCOUNT ON;BEGIN TRY THROW 60000, 'This a custom message!', 1; END TRYBEGIN CATCH THROW END CATCH

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I want to check a condition in the TRY block. How can I control the flow of execution and raise the error?

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Does the CATCH part automatically rollback the

statements within the TRY part?

CREATE PROC sptest AS SET NOCOUNT ON;BEGIN TRY CREATE TABLE dbo.Saeid --No1 ( id int ); SELECT 1/0 --No2END TRYBEGIN CATCH THROW END CATCHgo------------------------------------->

EXEC sptest;SELECT *FROM dbo.Saeid;

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Can someone use TRANSACTION in the TRY/CATCH block?

CREATE PROC sptest AS SET NOCOUNT ON;BEGIN TRY SET XACT_ABORT ON; --set xact_abort option BEGIN TRAN --begin transaction CREATE TABLE dbo.Hasani ( id int ); SELECT 1/0 COMMIT TRAN --commit transactionEND TRYBEGIN CATCH IF @@TRANCOUNT > 0 --check if there are open transaction? ROLLBACK TRAN; --rollback transaction THROW END CATCH------------------------------------->EXEC sptest;

SELECT *FROM dbo.Saeid;

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Can someone use TRANSACTION in the TRY/CATCH block?

TRY block• XACT_ABORT• Begin transaction• Statements to try

• Commit transactionCATCH block• Check @@TRANCOUNT and rollback all transactions• THROW

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See Also

Related TechNet Wiki Articles:

Error Handling within Triggers Using T-SQLT-SQL: Error Handling for CHECK Constraints

BOL link: http://technet.microsoft.com/en-us/library/ms175976.aspx